Add specific Nintendo 3DS features for the 3DS port

[Matriks404]

NOTE: Need to do #51 first.

General ideas:

• On main menu/other similar screens, display all usual info on the top screen, while interactive elements on the bottom one.
  • Add instructions option to see controls instructions etc.
• In the level editor display everything related to editing on the bottom screen, while any information that you can't directly control through touchscreen (or can be easily manipulated using physical buttons) display on the top one.
• In gameplay, in vertical levels, use specific screen as the default for each vertical area, with character freely going between the physical screens, unless it is outside of them, which updates viewport accordingly.
• In horizontal levels, when user goes to vase, the area with character should appear on the bottom screen, while the main area lays on the top screen (like New Super Mario Bros.).